I was also thinking of a K.I.S.S. system, depending on how much traction is needed and if the steering effort vs upper body strength of the operator are compatible:
Put ATV tires on it and voila! I mean, not that mower but a cart with fwd and 360 deg steering. Your controller could be a contactor switch.
P.S. As you can see the steering on this rig is geared down for low effort. Plus the lack of caster and the fact it's the drive wheel should make it low effort as well.